WCF Parameter Validation with Interceptor

Question

I have a WCF service with operations that all require MyServiceRequest parameter (or derived type) and returns MyServiceResponse (or dervived type), i.e.:

Answer 1

IParameterInspector can prevent operation from executing by throwing an exception. Here's an example.

Define a custom fault contract:

public class DataAccessFaultContract
{
    public string ErrorMessage { get; set; }
}

Then the inspector:

public class InspectorAttribute : Attribute, IParameterInspector, IOperationBehavior
{
    public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState)
    {

    }

    public object BeforeCall(string operationName, object[] inputs)
    {
        MyServiceRequest request = null;
        if (inputs != null && inputs.Length > 0)
        {
            request = inputs[0] as MyServiceRequest;
        }

        if (request != null && request.Username != "user" && request.Password != "secret")
        {
            var fc = new DataAccessFaultContract{ ErrorMessage = "Invalid user" };
            throw new FaultException(fc);
        }
        return null;
    }

    public void AddBindingParameters(OperationDescription operationDescription, BindingParameterCollection bindingParameters)
    {
    }

    public void ApplyClientBehavior(OperationDescription operationDescription, ClientOperation clientOperation)
    {
    }

    public void ApplyDispatchBehavior(OperationDescription operationDescription, DispatchOperation dispatchOperation)
    {
        dispatchOperation.ParameterInspectors.Add(this);
    }

    public void Validate(OperationDescription operationDescription)
    {
    }
}

And finally decorate your operation with appropriate attributes:

[ServiceContract]
public interface IMyServiceContract
{
    [Inspector]
    [FaultContract(typeof(DataAccessFaultContract))]
    [OperationContract]
    MySeviceResponse FindAppointments(FindAppointmentRequest request);

    ...
}

When invoking the service, the client could check for FaultException:

try
{
    var response = client.FindAppointments(request);
}
catch (FaultException ex)
{
    string errorMessage = ex.Detail.ErrorMessage;
    // ...
}